Laminated glass is very safe because it undergoes little ejection of glass fragments even when fractured by an external impact. As a consequence, laminated glass is widely employed as window glass in aircraft, buildings, vehicles such as automobiles, and so forth. An example of laminated glass is laminated glass provided by interposing, for example, an interlayer film for laminated glass comprising a plasticizer and a polyvinyl acetal resin, e.g., a polyvinyl butyral resin and so forth, between at least a pair of glass sheets and laminating and converting into a single body.
Reducing the thickness of laminated glass has been investigated in recent years in order to reduce the weight of laminated glass. A problem here, however, has been that a reduction in the thickness of laminated glass is associated with a reduction in the sound-insulating performance. When such a laminated glass is employed for the windshield, for example, of an automobile, a satisfactory sound-insulating performance is not obtained in the sound range at approximately 5000 Hz, e.g., wind noise, wiper operating noise, and so forth.
To counter this problem, Patent Document 1 discloses a laminated glass that is provided with a plurality of glass sheets and an interlayer film interposed within this plurality of glass sheets. This interlayer film has a sound-insulating layer comprising a polyvinyl acetal resin having a degree of acetalation of 60 to 85 mol %, an alkali metal salt or an alkaline-earth metal salt, and a plasticizer, wherein the plasticizer content is more than 30 parts by mass with respect to 100 parts by mass of the polyvinyl acetal resin and the content of the alkali metal salt or alkaline-earth metal salt is 0.001 to 1.0 part by mass with respect to 100 parts by mass of the polyvinyl acetal resin.
The laminated glass disclosed by Patent Document 1 is regarded as having an excellent sound-insulating performance. However, there exist both air-borne sound, e.g., vehicle noise, horn noise, and so forth, and solid-borne sound, e.g., sound due to the vibration of the vehicle engine and so forth, and the laminated glass described in Patent Document 1 has an inferior sound-insulating performance for solid-borne sound in an environment at or below 0° C.
Patent Document 1: Japanese Kokai Publication 2007-070200 (JP-A 2007-070200)